Spectacle lenses are distinguished between spectacle lenses having no nominal dioptric power and corrective spectacle lenses, i.e., spectacle lenses having dioptric power. According to DIN EN ISO 13666, dioptric power is the collective term for the focusing and the prismatic power of a spectacle lens.
In the case of corrective spectacle lenses, a distinction is also drawn between monofocal spectacle lenses and multifocal spectacle lenses. A monofocal spectacle lens is a spectacle lens in which there is only one dioptric power. A multifocal spectacle lens is a spectacle lens in which there are two or more different regions having different dioptric powers in the spectacle lens.
The shape that the spectacle lens has to adopt on its front face and/or reverse face in order to obtain the desired optical correction is determined to a crucial degree by the material from which the spectacle lens is manufactured. The most important parameter here is the refractive index of the material used. While spectacle lenses used to be produced predominantly from mineral glasses, especially crown glasses (Abbe number >55) and flint glasses (Abbe number <50), spectacle lenses made from a multitude of organic materials have now become available. The refractive index of the mineral glasses suitable for spectacle lenses may be higher than the refractive index of the organic materials usable for spectacle lenses. Particular features of spectacle lenses based on mineral glasses are their high scratch resistance and good chemical stability. By comparison, spectacle lenses based on organic materials have the particular features of lower specific weight and high fracture resistance.
Spectacle lenses based on mineral glasses are regularly produced by mechanically abrasive machining of a spectacle lens blank. In a spectacle lens blank, neither the front face nor the reverse face already corresponds to the ultimate, optically effective target faces. The optical face of a spectacle lens destined for arrangement on the object side is referred to as the front face; the optical face of a spectacle lens destined for arrangement on the eye side is referred to as the reverse face. The face between them, which either directly forms an edge or indirectly adjoins the front face at one end and the reverse face at the other end via an edge face, is referred to as cylinder edge face. The above-defined terms “front face,” “reverse face,” and “cylinder edge face” are used analogously hereinafter for semifinished spectacle lenses and finished spectacle lenses.
Spectacle lenses based on organic materials are cast, for example, as semifinished spectacle lenses with spherical, rotationally symmetric aspherical, or progressive front faces in mass production in prototypes with front face and reverse face mold shells that are spaced apart from one another by means of a sealing ring, forming a cavity, as described, for example, in JP 2008191186 A. The reverse face of a semifinished spectacle lens thus produced can, for example, be machined in a mechanically abrasive manner to obtain a finished spectacle lens.
Semifinished spectacle lenses, also referred to as semifinished products, are spectacle lens blanks having a front face or reverse face that already corresponds to the ultimate, optically effective target face. Finished spectacle lenses, also referred to as ready-made or finished products or ready-made spectacle lenses, are spectacle lenses having a front face and reverse face that is already the ultimate, optically effective target face. Finished spectacle lenses may, for example, either be cast as finished spectacle lenses, for example in prototypes with front and reverse face mold shells spaced apart from one another by means of a sealing ring, forming a cavity, or be manufactured by means of an Rx process. Finished spectacle lenses are generally also edged, i.e., converted to the ultimate shape and size matched to the spectacle frame by edge processing. Rx process is understood to mean the application-specific prescription manufacture in accordance with the prescription data for a spectacle wearer. The starting material used is semifinished spectacle lenses.
EP 0 182 503 A2 discloses an ophthalmic composite spectacle lens comprising a thin glass layer having a thickness of 0.5 mm to 2.0 mm on the object side and a plastic layer on the eye side. The glass layer and the plastic layer are bonded to one another by a highly elastic adhesive. The reverse face of the glass layer here has a different curvature than the front face of the plastic layer. The gap that arises as a result at the edge in particular is filled by the adhesive used.